Hydrogen is becoming the reference fuel for future transportation and the timetable for its adoption is shortening. However, to deploy its full potential, hydrogen production either directly or indirectly needs to satisfy three criteria: no associated emissions, including CO_2; wide availability; and affordability. This creates a window of great opportunity within the next 15 years for nuclear energy to provide the backbone of hydrogen-based energy systems. But nuclear must establish its hydrogen-generating role long before the widespread deployment of Gen Ⅳ high-temperature reactors, with their possibility of producing hydrogen directly by heat rather than electricity. For Gen Ⅳ the major factors will be efficiency and economic cost, particularly if centralised storage is needed and/or credits for avoided emissions and/or oxygen sales. In the interim, despite its apparently lower overall efficiency, water electrolysis is the only available technology today able to meet the first and second criteria. The third criterion includes costs of electrolysis and electricity. The primary requirements for affordable electrolysis are low capital cost and high utilisation. Consequently, the electricity supply must enable high utilisation as well as being itself low-cost and emissions-free. Evolved Gen Ⅲ+ nuclear technologies can produce electricity on large scales and at rates competitive with today's CO_2-emitting, fossil-fuelled technologies. As an example of electrolytic hydrogen's potential, we show competitive deployment in a typical competitive power market. Among the attractions of this approach are reactors supplying a base-loaded market - though permitting occasional, opportunistic diversion of electricity during price spikes on the power grid - and easy delivery of hydrogen to widely distributed users. Gen Ⅳ systems with multiple product streams and higher efficiency (e.g., the SCWR) can also be envisaged which can use competitive energy markets to advantage and produce hydrogen both centrally (directly) and distributed (indirectly).
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